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BIOC192 > Lecture 7: PROTEINS IN ACTION - 1 > Flashcards

Lecture 7: PROTEINS IN ACTION - 1 Flashcards

1
Q

What is the concentration of oxygen in saline solution limited to?

A

Approximately 0.2 mmol/L

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2
Q

What is the concentration of haemoglobin in blood?

A

Approximately 5 mmol/L

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3
Q

What does adding haemoglobin do?

A

Allows for delivery of much more oxygen

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4
Q

What is highly active tissue limited by?

A

Availability of oxygen

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5
Q

What is there strong evolutionary pressure for?

A

Efficient oxygen delivery

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6
Q

What type of protein is myoglobin?

A

Heme

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7
Q

What does myoglobin do?

A

Stores oxygen in muscles against bursts of high requirements

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8
Q

How much myoglobin does human muscle have?

A

0.5-0.7 mol/L which is enough for about 7 seconds of intense activity

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9
Q

What does the tissue depend on after the myoglobin store is exhausted?

A

Oxygen delivery from the lungs

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10
Q

What is the primary structure of myoglobin?

A

Approximately 150 amino acids

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11
Q

What is the secondary structure of myoglobin?

A

Eight alpha helices (A-H) and connecting loops (AB, BC, etc)

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12
Q

What is the tertiary structure of myoglobin?

A

Globin fold with a hydrophobic pocket

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13
Q

What does the heme bind to in the global protein in myoglobin?

A

His F8 (eight amino acid in helix F, which is a histidine)

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14
Q

What is the quaternary structure of myoglobin?

A

Monomeric (a single polypeptide chain)

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15
Q

What does the global fold in myoglobin do?

A

Provides a hydrophobic pocket (ValE11 and Phe CD7) to bind a heme group

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16
Q

What is heme?

A

A prosthetic group or cofactor

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17
Q

What is in the heme?

A

Four pyrrole rings linked together (a protoporphyrin) in a plane

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18
Q

What does iron have?

A

Six coordinate bonds - four to nitrogen atoms of the heme, one to a nitrogen atom of Histidine F8 of the globin, one to oxygen

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19
Q

What gives the heme a red colour?

A

Molecular electronic orbitals or protoporphyrin

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20
Q

What type of reaction is the binding of oxygen to iron?

A

Reversible

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21
Q

What doe spectroscopy do?

A

Quantify dissolved materials

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22
Q

What does higher concentration mean in spectroscopy?

A

Less transmitted light = higher absorbance

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23
Q

What does the beer-lambert law do?

A

Converts from absorbance to concentration

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24
Q

How are different wavelengths absorbed?

A

More or less effectively

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25
Q

What does the shape of the spectrum differ with?

A

Colour and chemical nature of the solute

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26
Q

What colour is protein?

A

Colourless (but has UV absorbance)

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27
Q

What does heme have?

A

Visible absorbance (and therefore colour) that differs between bright red oxyhemoglobin and dull red deoxyhaemoglobin

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28
Q

How is heme fe2+ attached to global protein?

A

By coordinate linkage to HisF8

29
Q

Where is another His located?

A

In helix E (hisE7) on the opposite side of the heme and distorts binding of gas molecules to 6th coordination position on fe2+

30
Q

What does hisE7 do?

A

Reduces the binding affinity of oxygen to myoglobin, making it easier to release oxygen to the muscle cell

31
Q

What does lactate do to myoglobin?

A

Decreases its affinity to oxygen but does not bind where oxygen binds. Allosteric control

32
Q

What does lactate cause to change in the curve of myoglobin?

A

Shifts the curve right

33
Q

What does lactate build up in muscles promote?

A

Oxygen release from myoglobin, increasing oxygen availability for respiration

34
Q

What does allosteric mean?

A

Without overlapping (not in the same place)

35
Q

What does the availability of oxygen to cellular respiration depend on?

A

The partial pressure of oxygen in the local environment and the binding affinity of oxygen to haemoglobin

36
Q

When is myoglobin saturated?

A

At low partial pressure of oxygen, only releasing oxygen to muscle cells when the cellular partial pressure of oxygen is very low

37
Q

How is the oxygen binding of myoglobin shown?

A

In a hyperbolic curve

38
Q

What does the oxygen binding of myoglobin suit?

A

Its function as a back up store of oxygen in muscle cells

39
Q

What is the partial pressure of oxygen in lungs?

A

Approximately 100 torr

40
Q

What is the partial pressure of oxygen in resting muscle?

A

Approximately 20 torr

41
Q

What is the function of haemoglobin?

A

An oxygen transporter in blood and has much weaker binding affinity for oxygen than myoglobin

42
Q

How is the oxygen binding of haemoglobin shown?

A

As a sigmoidal curve

43
Q

What does haemoglobin in red blood cells in the blood need to be able to do?

A

Bind oxygen in the vicinity of the lungs and release oxygen in the vicinity of peripheral tissues

44
Q

What did haemoglobin evolve to do?

A

Bind oxygen less tightly than myoglobin

45
Q

What can haemoglobin do?

A

Change shape, “dumping” oxygen in peripheral tissues

46
Q

What structure did haemoglobin evolve?

A

To be a tetramer - four global proteins associate together non-covalently

47
Q

What does each global protein in haemoglobin contain?

A

One heme and each can bind one oxygen (1, 2, 3, or 4 oxygen can bind per one haemoglobin tetramer)

48
Q

What is the structure of myoglobin?

A

Monomer

49
Q

The structures of oxyhemoglobin and deoxyhaemoglobin are…

A

Similar but different

50
Q

What does MWC in the concerted model stand for?

A

Monod, Wyman and Changeux

51
Q

What conformations can subunits be in?

A

Low activity, tense (T) or high activity, relaxed (R)

52
Q

What must all subunits be in?

A

The same state (T or R)

53
Q

What does binding each successive substrate do?

A

Shift the equilibrium in favour of R

54
Q

What stabilises the T form?

A

Inhibitors

55
Q

What stabilises the R form?

A

Activators

56
Q

What does KNF stand for in the sequential model?

A

Koshland, Nemethe and Filmer

57
Q

What does only one substrate binding do in the sequential model?

A

Induces a T to R conformational change in only one subunits

58
Q

What does the conformational change in the sequential model do?

A

Influences the neighbouring subunit (cooperativity), making them more likely to bind substrate. Many conformations possible

59
Q

What does the sequential model explain?

A

Negative cooperativity

60
Q

What does oxygen do in myoglobin and haemoglobin?

A

Binds to the iron of heme

61
Q

What happens in myoglobin and haemoglobin to monitor oxygen binding?

A

A shift from dull to bright red

62
Q

What happens to the affinity of oxygen in myoglobin and haemoglobin?

A

It is altered by molecules (such as lactate to myoglobin) binding elsewhere (allosteric control)

63
Q

What is the difference in myoglobin and haemoglobin in structure?

A

Monomer vs tetramer

64
Q

What is the difference in myoglobin and haemoglobin in binding curve?

A

Tighter hyperbolic vs weaker sigmoidal

65
Q

What is the difference in myoglobin and haemoglobin in function?

A

Stored in tissue vs transport molecule

66
Q

What does cooperativity require?

A

Multiple interacting subunits

67
Q

What binding curve does cooperativity give?

A

A sigmoidal curve

68
Q

What does cooperativity do to binding affinity?

A

Shifts binding affinity (steep part of binding curve) to a physiologically relevant oxygen concentration

BIOC192 (38 decks)

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